Effect of refractive index-mismatch on laser microfabrication in silica glass

We studied the peculiarities of femtosecond laser microfabrication in silica glass with a refractive index that did not exactly match the value for which the focusing optics is designed. Spherical aberrations resulting from a small refractive index mismatch were found to increase the size and distort the shape of photodamaged regions, thus reducing the spatial resolution of the microfabrication. However, these undesirable effects can be minimized, providing that the focusing depth inside the glass is not too large, and the laser intensity is kept close to the light-induced damage threshold. Received: 3 December 2001 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +81-88/656-7598, E-mail: misawa@eco.tokushima-u.ac.jp     

Phase separation and partial devitrification in soda-lime silicate glasses

2 O-rich droplets dispersed throughout the SiO₂-rich matrix and nanoparticles of metallic silver. In exchanged specimens the joint effect of colloidal silver and electric field results in partial transformation of the amorphous droplets into crystalline Na₂O particles. Received: 11 February 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999     

Modification of rubber surface by UV surface grafting

Rubber surface is subjected to ultraviolet radiation (UV) in the presence of allylamine and radiation sensitizer benzophenone (BP). Fourier transform infrared spectral studies reveal the presence of allylamine on the surface. The presence of irregular needle shapes on the surface as observed in scanning electron micrographs also confirms the polymerized allylamine on the surface. Allylamine coatings have been further confirmed from atomic force microscopy (AFM) analysis. Thermogravimetric analysis (TGA) reveals that allylamine coating on the rubber surface lowers the thermal degradation rate. The contact angle between the water and rubber surface decreases for the modified rubber surface confirming the surface modification due to UV surface grafting.     

Molar volume and compactness versus mean coordination number in GeSeFe glasses: observation of a threshold behavior

Molar volumes, V, and compactness values, α, of 34 glassy compositions of the GeSeFe system have been obtained using their measured densities. The property–composition dependences are examined in light of the models proposed for the structure of these network glasses. Received: 28 August 2000 / Accepted: 9 January 2001 / Published online: 23 March 2001     

The morphologies of fractured surfaces and fracture toughness in some As-Se-Sb-S-I glasses

As part of a general physical characterization of amorphous materials in the pseudobinary system (As₂Se₃)_100−x(SbSI)_x type, their indentation fracture toughness was determined. It is a system with the variable ratio of classical amorphous compound As₂Se₃ and the molecule of antimony sulfoiodide, SbSI, which in the monocrystal form is characterized as ferroelectrics. Because of chalcogenides are generally very brittle and under load they crack very easily, these glasses have been studied with the aim of examining the possibility of obtaining some new structures on the basis of the materials with amorphous internal network, the structures that will have a higher quality in respect of mechanical properties. The morphologies of fractured surfaces were investigated by scanning electron microscope.     

Transmission electron microscopy studies of femtosecond laser induced modifications in quartz

Cross-sectional transmission electron microscopy investigations of femtosecond laser induced sub-micrometer structural modifications inside crystalline quartz were carried out. Modifications from single laser shots and from lines built of overlapping shots were imaged. Both single laser shot modifications and line structures show an amorphous core surrounded by a disturbed crystalline structure. A strong strain field surrounding the central, irradiated, core is responsible for an increase of the refractive index. Finite element method calculations of the strain field show maxima on both sides of the irradiated core, which are in good agreement with optical measurements of the refractive-index change. Received: 29 September 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +49-3641/947792, E-mail: tatiana.gorelik@rz.uni-jena.de     

Incubation of laser ablation in fused silica with 5-fs pulses

The threshold fluences for laser-induced damage of fused silica with single 5-fs pulses from a Ti:sapphire laser system were determined by extrapolating the ablated volume to zero. These thresholds are about 4 times as high as the values previously obtained from multi-shot experiments. This result is interpreted in terms of an irreversible modification of the original material below the single-shot threshold (incubation). Received: 14 June 1999 / Accepted: 24 June 1999 / Published online: 8 September 1999     

The effect of compositional variations on the glass-transition and crystallisation temperatures in Ge-Se-In glasses

The glass-transition (T_g) and crystallisation (T_x) temperatures of glassy Ge_xSe_yIn₁₂ (7≤x≤28) have been determined from differential scanning calorimetry measurements. The variations of T_g and T_x with composition have been specified. It has been found that T_g reaches a maximum at 614 K for the composition Ge_23.33 Se_64.67 In₁₂ while T_x passes through a minimum at 740 K for the same composition. The values of the cohesive energies of the studied compositions have also been estimated using the chemical bond approach method. It is found that the composition Ge_23.33Se_64.67In₁₂ possesses the maximum cohesive energy. These results are explained in terms of the structure of Ge-Se-In glasses. Received: 12 March 2001 / Accepted: 29 March 2001 / Published online: 23 May 2001     

Long-term existence of a solid surface under temperature above melting point. Is it possible?

Received: 21 November 1997/Accepted: 1 April 1998     

Surface morphology of MgO (100) crystals implanted with MeV Al+ and Al2+ ions

MgO (100) single crystals are implanted with 1.50-MeV Al⁺ and 3.00-MeV Al₂ ⁺ ions at a fluence of 1×10¹⁵ Al  atoms  cm^-2 under high-vacuum conditions. The surface morphology of the substrate is measured in air using atomic force microscopy and X-ray reflectometry followed by computer-simulated spectrum analysis. The ion-irradiated areas are found to protrude to different heights on the nanometre scale. Small height differences are observed in the areas irradiated by Al⁺ and Al₂ ⁺ ions of comparable energy, dose rate and total fluence. The results indicate that protrusions are most likely caused by implantation-induced point defects (vacancies) generated in the crystal during implantation. Other possibilities for the cause of protrusions are discussed. Thermal treatment stimulates a partial recovery of the implantation damage and alters the topography of MgO surfaces. Received: 22 May 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Absorption and emission properties of Nd in lithium cesium mixed alkali borate glasses

Lithium cesium mixed alkali borate glasses of the composition 67B₂O₃·xLi₂O·(32−x)Cs₂O (where x=8, 12, 16, 20 and 24) containing 1 mol% Nd₂O₃ were prepared by melt quenching. The absorption spectra of Nd³⁺ were studied from the experimental oscillator strengths and the Judd-Ofelt intensity parameters were obtained. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) (A_T), branching ratios (β) and integrated absorption cross-sections (Σ) of the Nd³⁺ transitions from the excited state J manifolds to the lower lying J′ manifolds. Radiative lifetimes (τ_R) are estimated for certain excited states of Nd³⁺ in these mixed alkali borate glasses. Luminescence spectra were measured and the emission cross-sections (σ_p) were evaluated for the three emission transitions. The variation of luminescence intensity with x was recorded for the three transitions at different excitation power to see the effect of mixed alkalies in these borate glasses.     

Local atomic structures in Zr-Ni metallic glasses

Local atomic structures of Zr100−xNix (x=33.3, 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr-Ni bond length, RZr-Ni, keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr₆₄Ni₃₆ metallic glass consist of Zr₂Ni-like and ZrNi-like CSROs.     

Orientation studies of Si-phthalocyanine sulfonic acids cast on SiOx substrates

Layers of dihydroxy silicon phthalocyanine tetrasulfonic acid and oligo-μ-oxo silicon phthalocyanine tetrasulfonic acid were prepared by solution-casting methods. The purity of the material was checked by X-ray photoemission spectroscopy. The orientation of the molecules in respect to the substrate plane was investigated by angle-dependent near-edge X-ray absorption fine-structure spectroscopy. The morphology was characterized by atomic force microscopy. Most samples exhibited a significant orientation that was accompanied by crystalline structures; others had no orientation at all with a dominant amorphous morphology. This behavior indicates that several preparation parameters affect the crystallinity and the orientation of the phthalocyanines. Received: 16 January 2002 / Accepted: 11 February 2002 / Published online: 3 May 2002 RID="*" ID="*"Corresponding author. Fax: +1-919/515-7331, E-mail: harald_ade@ncsu.edu RID="**" ID="**"Present address: Southern Illinois University, Physics, Mailcode 4401, Carbondale, IL 62901, USA     

Precision laser ablation of dielectrics in the 10-fs regime

Received: 4 January 1999 / Accepted: 5 January 1999     

Numerical studies of the vibrational isocoordinate rule in chalcogenide glasses

Many properties of alloyed chalcogenide glasses can be closely correlated with the average coordination of these compounds. This is the case, for example, of the ultrasonic constants, dilatometric softening temperature and the vibrational densities of states. What is striking, however, is that, at a given average coordination, these properties are nevertheless almost independent of the elemental composition. Here, we report on some numerical verification of this experimental rule as applied to the vibrational density of states. We find that this rule is not exact but holds qualitatively well over a wide range of compositions and local chemical correlations. Received 25 April 2000     

Threshold electrical switching in As45Te55-xInx and As50Te50-xInx glasses

The electrical switching behaviour of As₄₅Te_55-xIn_x (5≤x≤15) and As₅₀Te_50-xIn_x (2.5≤x≤11.5) has been studied over a wide range of compositions. These glasses are found to exhibit threshold switching. The composition dependence of switching voltage (V_t) has been found to exhibit a change in slope and a local minimum at compositions x=10 and 12.5 for As₄₅Te_55-xIn_x and x=7.5 and 10.8 for As₅₀Te_50-xIn_x, respectively. The slope change in V_t verses x and the local minimum have been identified using two network topological effects, namely the rigidity percolation threshold and the chemical threshold. Received: 23 August 2001 / Accepted: 27 August 2001 / Published online: 11 February 2002     

Molecular dynamics simulation of ternary glasses Li2O-P2O5-LiCl

Molecular dynamics simulation of binary glass 52Li₂O-48P₂O₅ and ternary glasses 45Li₂O-42P₂O₅-13LiCl and 39Li₂O-36P₂O₅-25LiCl was undertaken to study the effects of the addition of LiCl to the binary phosphate glass. The results show that addition of LiCl in the glass creates more non-bridging oxygens and reduces P-O-P chain lengths and branches in these chains, leading to a weakening of the glass matrix and consequent lowering of T_g. Interchain linkages mediated by Li in the binary structure diminish, and consequently better channels are created for Li⁺ movement, enhancing the ionic conductivity σ. Structure parameters also indicate the absence of LiCl clusters in the glass matrix.     

Dynamic scanning force microscopy study of self-assembled DNA-protein nanostructures

Self-assembled oligomeric nanostructures consisting of bisbiotinylated DNA fragments connected by the protein streptavidin (STV) are studied by dynamic scanning force microscopy (SFM) operating in air. A comparison of the images taken in repulsive and attractive regimes is systematically made on DNA and STV structures. Stable and reproducible SFM images are obtained in the attractive regime by using a special feedback circuit, called Q-control. On the other hand, when SFM is operating in the repulsive regime, deformation of the structures that reduce the resolution and the image quality are clearly observable. The heights of both DNA and STV have been measured as a function of the tip/molecule interaction forces. This study offers the possibility to suggest a different mechanical behavior of DNA with respect to STV. Received: 24 July 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Formation of Si structure in glass with a femtosecond laser

Mixing metallic Al into the starting material for silicate glass is proposed as a means of forming Si structures in glass. We confirmed that Si nanocrystals are space-selectively deposited in silicate glass via a thermite reaction triggered by femtosecond laser pulses. Small Si particles were transformed into larger, but still micrometer sized, Si particles by laser irradiation. These structures grew to micro-size particles due to the thermite reaction promoted by heat treatment. We discuss what effect the irradiation of the focused laser pulse had on the Si deposition process in the laser-irradiated region. Localized high temperatures and pressures and generation of shock waves appear to be very important in forming Si-rich structures that contribute to the growth of Si particles. The diffusion of calcium ions by the generation of shock waves and the presence of Al-rich structures is important for forming Si-rich structures such as Si clusters, which is achieved by continuously breaking Si–O bonds using localized high temperatures.